This invention relates generally to gas turbine engine inspection port openings and, more particularly, to borescope plugs used to seal gas turbine engine inspection port openings.
Gas turbine engines often include spaced apart walls or casings that include opposing openings sealed with removable seals. The seals are removable to permit inspection equipment to access engine components housed within the casings. The spaced apart walls include an inner wall and an outer wall. The inner wall is subjected to greater temperatures than the opposed outer wall during gas turbine engine operation which results in differential thermal expansion. The spaced apart openings therefore may become misaligned during engine operation causing leakage through at least one of the openings. Hot gases that escape through the inspection port openings may cause damage to other engine components.
To reduce seal leakage, and more specifically, to accommodate the differential thermal growth described above, known borescope plugs include a spring and a plunger. A first end of the plunger is housed within a housing surrounding a first inspection port opening, and includes a ball and swivel joint that permits the plunger to swivel while maintaining sealing contact with the first inspection port opening. A first end of the spring is tapered to maintain contact with the swivel joint and a second end of the spring maintains the plunger in sealing contact against a second inspection port opening.
As the engine operates, the borescope plug moves in proportion to differential thermal expansion of the walls. During engine operation temperature changes, as temperatures increase, the borescope plug plunger second end may shift abruptly in response to thermal expansion of the second wall causing the plunger first end to bind. As the spring second end continues to move, the spring first end may become unseated from the ball joint and become wedged against the plunger. Over time, continued contact between the spring and the plunger may cause damage to the plunger and shorten the useful life of the borescope plug.
In an exemplary embodiment, a borescope plug for a gas turbine engine includes a retainer that facilitates extending the useful life of the borescope plug. The borescope plug seals a pair of opposing inspection port openings in at least two respective spaced-apart walls despite differential thermal growth between the two walls. The borescope plug includes the retainer, a plunger, and a biasing mechanism. The plunger extends through the biasing mechanism and the retainer.
In use, the biasing mechanism biases the plunger to maintain sealing contact against one of the inspection port openings despite differential thermal growth between the spaced-apart walls. The retainer contacts the substantially cylindrical biasing mechanism and maintains a position of the biasing mechanism relative to the plunger. Accordingly, the retainer prevents the biasing mechanism from contacting the plunger. As a result, the borescope plug retainer facilitates extending the useful life of the plunger and the borescope plug in a cost effective and reliable manner.